The present invention mainly relates to a tension structure of a seat back which increases a supporting pressure of a lumbar part more than a supporting pressure between a waist part and a shoulder part of a sitter, in order to construct a seat back of a seat for an automotive vehicle having an improved sitting characteristic by intending to stabilize a sitting attitude.
In general, in the seat back of the seat for the automotive vehicle, a tension structure which supports between a the lumbar part and a back part of the sitter is constructed by providing with a seat back frame having a substantially quadrilateral frame shape, and assembling a tension assembly constituted by a cushion spring or a lumbar support within the seat back frame.
Among the cushion spring and the lumbar support, the cushion spring is exemplified. The cushion spring is constructed as the tension assembly by bridging a plurality of narrow wires or zigzag springs between right and left vertical bars in a parallel manner. The cushion spring is assembled within the seat back frame by being tensioned and held by tension members which are bridged over an upper portion, a lower portion and a middle portion between each of side frame portions of the seat back frame and each of axes of the vertical bars.
Conventionally, the tension members are assembled in all of the upper portion, the lower portion and the middle portion in such a manner as to be provided with coil springs having the same spring rate and tension and hold the cushion spring with respect to each of the side frame portions in the seat back frame.
In accordance with the coil spring, since the cushion spring is largely elastically displaced due to a load of the sitter, a great displacement stroke can be obtained by the cushion spring.
In this case, in the seat back of the seat for the automotive vehicle, since the lumbar part holding characteristic can be applied by making the supporting pressure of the portion corresponding to the lumbar part higher than the supporting pressure of the portion corresponding to a portion between the waist part and the shoulder part of the sitter, even when the portion between the waist part and the shoulder part of the sitter is largely elastically displaced, it is possible to intend to stabilize a sitting attitude and it is possible to construct a structure having an improved sitting characteristic.
However, in the tension structure by the coil springs having the same spring rate as mentioned above, the supporting pressure of the portion corresponding to the lumbar part can not be made higher than the portion between the waist part and the shoulder part of the sitter.
In this case, in order to increase the supporting pressure of the portion corresponding to the lumbar part, there can be considered a structure of tensioning and holding the portion corresponding to the lumbar part by a coil spring having a higher spring rate than that of the coil spring which tensions and holds the portion between the waist part and the shoulder part of the sitter.
In this case, since it is necessary to prepare the other coil spring having the different spring rate by using the coil spring in accordance with the same aspect, a cost increased is caused. In addition, since it is necessary to perform an assembling operation while differentiating the coil springs on the basis of the difference of the spring rate, an operation becomes complex.
An object of the present invention is to provide a tension structure of a seat back which can keep an improved cushion characteristic and can be assembled so as to increase a supporting pressure of a lumbar part without causing a cost increase and a complex operation by paying attention to a tension member of a tension assembly.
Further, another object of the present invention is to provide a tension structure of a seat back which can be securely assembled in accordance with a simple operation so as to increase a supporting pressure of a lumbar part.
The present invention is provided with coil springs having the same spring rate, as tension members between side frame portions of a seat back frame and vertical bars of a tension assembly in upper portions and middle portions in the respective side frame portions and the respective vertical bars. On the contrary, a tension structure of a seat back is constructed by providing a linear wire which is obtained by entwining and fastening one wire end which is bent in a predetermined axial shape to an axis of the vertical bar and inserting and fastening another wire end which is bent in a predetermined axial shape to a stop ring in the side frame portion, in a lower portion, and tensioning and holding the tension assembly within the seat back frame by the coil springs in the upper portion and the middle portion and the linear wire in the lower portion.
Accordingly, with respect to the portion corresponding to the region between the waist part and the shoulder part of the sitter, an improved cushion characteristic can be kept by the coil spring which is elastically compressed and expanded, and with respect to the portion corresponding to the lumbar part, a degree of elastic displacement is restricted by the linear wire which is not expanded. Accordingly, since it is possible to increase the supporting pressure of the lumbar part and it is possible to achieve a stability of the sitting attitude, it is possible to construct the tension structure of the seat back having an improved sitting characteristic.
In addition, since the linear wire is inexpensive, causes no cost increase, and is different in aspect from the coil spring, it is easy to distinguish both of the elements. Accordingly, it is possible to perform an assembling operation with accompanying no troublesome of the operation.
Further, the present invention is provided with a linear wire constituted by a linear wire main axis which extends from the side frame portion of the seat back frame toward an oblique lower side with an acute angle to an axis of the vertical bar, a wire end which is bent at an acute angle from the wire main axis and is inserted to the stop ring of the side frame portion so as to be stopped, a substantially semicircular winding axis which is retained to the axis of the vertical bar, and a wire end which extends from the winding axis and intersects on the axis of the wire main axis.
The linear wire can be bridged between each of the side frame portions of the seat back frame and each of the vertical bars of the tension assembly in accordance with a simple operation of inserting one wire end to the stop ring of the side frame portion, deforming the wire end which intersects on the axis of the wire main axis wider than the wire main axis so as to retain the substantially semicircular winding axis to the axis of the vertical bar, and elastically returning back the wire end which intersects on the axis of the wire main axis. In the retaining state, since the winding axis of the linear wire is brought into contact with the axis of the vertical bar at two contact points which are obliquely apart from each other via the axis of the vertical bar, the linear wire can be securely retained to the axis of the vertical bar so that the winding axis does not deflected and moved vertically in the axial direction of the vertical bar, and can stably tension and hold the lower portion of the tension assembly.
The other features than the features mentioned above will be apparent from an embodiment for carrying out the invention which will be described later.